Biology 1002B Lecture Notes - Intermembrane Space, Cytoplasm, Citric Acid

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17 Apr 2012
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Lecture 10 Cellular Respiration
Cellular Respiration occurs in every living thing, maybe not the whole path tho
Photosynthesis is the major process that fixes carbon
Cellular Respiration is the major path that converts it into energy
Metabolic Pathways
Catabolic Pathways - ΔG will be negative (energy is released)
- Not every individual step will have a negative G
Ex. Cellular Respiration (Exergonic)
Anabolic Pathways - ΔG will be positive (low energy high energy)
- Not every individual step will have a positive G
Ex. Photosynthesis (Endergonic)
These pathways have a number of steps with an overall goal
ATP/ADP Cycle
The energy put in to form ATP is from a catabolic Pathway
The energy released from ATP is from a anabolic pathway
This is the energy currency of the cell
ATP is the form of energy that cells use
You use the energy from catabolic pathways to drive anabolic
pathways
Food as Fuel
C H Bonds have lots of energy associated with them
Neither are strongly electronegative, electrons are easily stolen
We talk about glucose as it goes through the whole respiratory
pathway
You can break down fatty acids/proteins as well
Cellular Respiration is a redox reaction
Respiration is Controlled Combustion
Respiration
Small activation energy
Enzyme catalyzed reactions
Energy is transferred to energy carriers
Direct Burning
Large Activation Energy Required
All Energy is released as heat… nothing is stored!
NAD+ as an electron shuttle
This is an electron shuttle molecule
Catabolic processes such as Respiration use NAD+
Anabolic processes such as Photosynthesis use NADP+
They are both 2 electron carriers
They do not fit into the same active site
H atom and 2 e- from food are transferred to NAD+
Note: Either way… the total possible energy
that can be obtained is 686 Kcal/mol
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Respiration Overview
Where is it found and what does it do?
What’s at the start? What about the end?
What is the change in potential energy in each of these
steps
What steps require Oxygen? Why?
Where is the carbon? Where is it released?
Glycolysis I: Energy Investment
The most ancient biochemical pathway in a cell
Occurs in the cytosol
Everything alive has glycolysis
In the first step you are actually consuming ATP
Interesting that we use ATP, when the goal is to create
ATP… why phosphorylate?
This makes the molecule more reactive (glucose
molecule)
It also places a negative charge on glucose, which
prevents it from passing through the membrane. Glucose
becomes ‘stuck’
Glycolysis II: Energy Payoff
One Molecule of Glucose gives two pyruvate
You make two NADH, Four ATP, and Two Pyruvate
Two molecules of pyruvate have less free energy than
glucose
Substrate level phosphorylation (one of two ways ATP is
made)
o Transfer of phosphate group of substrate onto ATP
No requirement for oxygen! This is an ancient pathway
Pyruvate still holds energy
Linking Glycolysis and the Citric Acid Cycle
Glycolysis occurs in the cytosol and pyruvate, the end product
is then transferred into the mitochondrial Matrix
Only Eukaryotic cells have a mitochondria, but
prokaryotes still use this pathway
You can’t equate cellular respiration with only eukaryotes!
There is a decarboxylation reaction (releases O2) as
pyruvate crosses the membrane into the mitochondrial
matrix
Then an enzyme called Dehydrogenase removes a
hydrogen to create an NADH
Glycolysis Pyruvate Oxidation Electron Transfer System
Glucose Acetyl-CoA Oxidative Phosphorylation
Pyruvate Citric Acid Cycle ATP
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The remainder of this molecule reacts with Coenzyme A, which makes the molecule
more reactive
This new molecule is called Acetyl CoA
This is called the Pyruvate Dehydrogenase Complex
Disorders of Energy Metabolism
“Inborn Errors of Metabolism’ is a mutation somewhere in the metabolic pathway
One of these mutations is ‘pyruvate dehydrogenase deficiency’ which prevents the
production of Acetyl CoA
Causes severe mental retardation… not enough ATP to support the brain
The brain is a HUGE ATP HOG
This condition can be overcome by a ‘Ketogenic Diet’
o 88% fat, 10% protein, 2% carbohydrate
o Forces the body/liver to use fats as a source of energy to the brain, changing the
bodies metabolism
Metabolic Pathways may shift from one
way to another:
o Lactate/Pyruvate Ratio
o ATP/ADP Ratio
o NAD/NADH Ratio
The Citric Acid Cycle
The Citric Acid Cycle/The Krebs Cycle
CoA acts as a delivery service
Energy is created in 3 different forms
After this cycle, there are no more
carbons to play with
You cell doesn’t use those types of
energy and you must convert it
The goal is to create ATP from food molecules
Not Just Glucose
Cellular Respiration is not just for glucose
Glucose simply shows the full pathway and so we
use it as an example
There are C H Bonds in Fats and Proteins
Where do Fatty Acids enter the Pathway?
Where do proteins enter the pathway?
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